SQLFluff only ever reports 1 issue

[tdstark]

Describe the bug
Regardless of the number of linting issues uncovered by SQLFluff, Megalinter only ever identifies that there is a maximum of one issue when run as part of Github Actions. This is a problem because SQL_SQLFLUFF_DISABLE_ERRORS_IF_LESS_THAN becomes redundant.

To Reproduce
Steps to reproduce the behavior:

1. Add the Github Actions config provided below to a .build file
2. Add problematic Redshift sql to project
3. Allow Megalinter to run SQLFluff

Expected behavior
Megalinter should flag one issue per issue identified by SQLFluff.

Screenshots
+----SUMMARY-+----------+---------------+-------+-------+--------+--------------+
| Descriptor | Linter | Mode | Files | Fixed | Errors | Elapsed time |
+------------+----------+---------------+-------+-------+--------+--------------+
| ❌ SQL | sqlfluff | list_of_files | 247 | | 1 | 1.34s |
+------------+----------+---------------+-------+-------+--------+--------------+

Additional context
Here is my Github Actions config snippet:

  lint_sql:
    name: Lint SQL
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v2

      - name: sqlfluff_redshift
        uses: megalinter/megalinter/flavors/python@v5
        env:
          DEFAULT_BRANCH: master
          GITHUB_TOKEN: ${{ secrets.CII_GITHUB_DEPLOYMENT_TOKEN }}
          GITHUB_COMMENT_REPORTER: false
          PRINT_ALPACA: false
          VALIDATE_SQL_SQLFLUFF: true
          SQL_SQLFLUFF_ARGUMENTS: --dialect=redshift

[nvuillam]

Some of the linters are not configured yet to list the number of errors, so it always displays one
This is the case for sqlfluff

https://github.com/megalinter/megalinter/blob/ffce8af23f5d2ba5d7555f23c30fd4107c22ec5b/megalinter/descriptors/sql.megalinter-descriptor.yml#L26

This can be done configuring descriptors properties cli_lint_errors_count and cli_lint_errors_regex ( example ) that are used to count the errors from output text file

Maybe you would like to make a PR ?

If not, myself or another contributor can do it someday :)

[tdstark]

I can take a stab at a PR.